The sense of hearing in human beings involves the use of hair cells in the cochlea that convert or transduce audio signals into auditory nerve impulses. Hearing loss, which may be due to many different causes, is generally of two types: conductive and sensorineural. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded. These sound pathways may be impeded, for example, by damage to the auditory ossicles. Conductive hearing loss may often be helped by the use of conventional hearing aids that amplify sound so that audio signals reach the cochlea and the hair cells. Some types of conductive hearing loss may also be treated by surgical procedures.
Sensorineural hearing loss, on the other hand, is due to the absence or the destruction of the hair cells in the cochlea which are needed to transduce audio signals into auditory nerve impulses. Thus, many people who suffer from severe to profound sensorineural hearing loss are unable to derive any benefit from conventional hearing aid systems. To overcome sensorineural hearing loss, numerous cochlear implant systems, or cochlear prosthesis, have been developed. Cochlear implant systems bypass the hair cells in the cochlea by presenting electrical stimulation directly to the auditory nerve fibers. Direct stimulation of the auditory nerve fibers leads to the perception of sound in the brain and at least partial restoration of hearing function.
Cochlear implant systems typically include a cochlear stimulator that is implanted beneath the scalp of a patient. An external control assembly located external to the patient's scalp is typically used to control and adjust various operational parameters of the implanted cochlear stimulator. An inductive link is used to transmit telemetry signals from the external control assembly to the implanted cochlear stimulator. In a conventional cochlear implant system, the external control assembly typically includes sound processing circuitry as well a battery that is used to power the implanted cochlear stimulator. Power is typically transferred through the scalp to the implanted cochlear stimulator via the inductive link. The external control assembly is often housed within a behind-the-ear unit and/or within a carrying case that can be attached to clothing worn by the patient.
One drawback associated with conventional cochlear implant systems is that their external control assemblies are powered by batteries, which are typically large, bulky, and relatively heavy due to the fact they must be sufficiently large to provide power for extended periods of time. Additionally, a conventional cochlear implant system is typically limited to a specific physical configuration, particularly with respect to the implanted components. Once a cochlear implant patient has been fitted with a cochlear implant system, the patient typically has to have the system surgically removed in order to change its physical configuration. Such procedures are invasive, costly, and undesirable.